Field of the Invention
The charging is carried out by magnetic induction: in a location called the “charging area”, a current is made to flow in a ground circuit having a transmitter coil, or primary, supplying power to a receiver coil, or secondary, in an electric or hybrid motor vehicle, hereinafter referred to simply as a “vehicle”.
The magnetic induction phenomenon takes place only if the primary and secondary coils are sufficiently close to one another, and the transmitted power depends to some extent on the resonance of the ground circuit. Although the vehicle is stationary while being charged, the frequency of the current flowing in the circuit must be adapted according to the position of the secondary relative to the primary, and therefore according to the position of the vehicle in the charging area relative to the primary (stationary) coil. The purpose of this is to achieve resonance of the system.
Thus, more precisely, according to a first of its objects, the invention concerns a method of contactless charging of a battery of an electric motor vehicle by magnetic induction between a resonant transmitter circuit comprising a transmitter coil of a charging device and a resonant receiver circuit of the vehicle comprising a receiver coil, the vehicle being positioned above the transmitter coil so as to provide magnetic coupling between the transmitter coil and the receiver coil, the method comprising steps consisting of:                controlling the electrical power supply and the instructions of an inverter to the terminals of which the transmitter coil is connected according to a variable frequency,        measuring in an analog circuit at least one analog signal relating to a current or to a voltage across the terminals of the transmitter coil.        
Description of Related Art
A method of this kind is known to those skilled in the art, notably from the example provided by the prior art document EP2317624 which proposes, notably, to compare phases between the voltage and the current in order to control the excitation frequency, in a circuit having a “phase comparator” module, on the basis of logic signals which are images of the sign of the current and the voltage, in order to generate a signal whose variable amplitude causes a variation in the excitation frequency by means of a VCO (standing for the English “Voltage Controlled Oscillator”) module, that is to say a voltage controlled oscillator which generates a signal whose frequency depends on the input voltage.
Other solutions consist in varying the frequency of the charging circuit as a function of the power received at the secondary; in this case, however, the vehicle battery may refuse an excessive power transfer.
However, these solutions are complicated and costly to implement.